Selective Adsorption Mechanism of Sebacoyl Hydroxamic Acid in the Flotation Separation of Scheelite from Fluorite: Experiments and DFT Calculations

Scheelite (CaWO₄) and fluorite (CaF₂) have similar surface physicochemical properties, resulting in poor flotation selectivity when using conventional fatty acid collectors (i.e., oleate (HOL)), and making it difficult to separate them efficiently. To address this challenge, a dual-ligand hydroxamic acid surfactant, sebacoyl hydroxamic acid (SHA), which contains two hydroxamic acid groups, was synthesized in this study as a novel collector to efficiently enrich scheelite from fluorite. Microflotation experiments showed that the recovery of scheelite with 40 mg/L SHA at pH = 8 was 93%, and that of fluorite was only 37%. In the artificial mixed ore flotation test, the scheelite concentrate with a WO₃ grade of 62.47% and a WO₃ recovery of 93.61% was obtained by using SHA, which was significantly better than that acquired from the HOL system. Contact angle tests showed that SHA could significantly enhance the surface hydrophobicity of scheelite at a low concentration, and its separation effect was better than that of HOL. FT-IR analysis and ζ-potential measurements exhibited that SHA had strong chemisorption behavior on the scheelite surface but not on the fluorite surface. XPS analysis and DFT calculations indicated that the -CONHOH groups of SHA could chelate with the Ca sites on the scheelite surface to form a five-membered ring. In addition, SHA has stronger chemical reactivity and van der Waals forces for scheelite than HOL.